A traveling wave tube, a klystron and the like are electron tubes which are used for performing amplification, oscillation and the like of an RF (Radio Frequency) signal through interactions of electron beams emitted from an electron gun with a high frequency circuit.
As shown in FIG. 1, traveling wave tube 1 comprises, for example, electron gun 10 for emitting electron beam 50, helix 20 which is a high frequency circuit for causing electron beam 50 emitted from electron gun 10 to interact with an RF signal, a collector 30 for capturing an electron beam 50 emitted from electron gun 10, and anode 40 for drawing electrons from electron gun 10 and guiding electron beam 50 emitted from electron gun 10 into spiral helix 20. Electron gun 10 comprises cathode 11 for emitting hot electrons, and heater 12 for giving thermal energy to cathode 11 for causing the same to emit hot electrons.
Electron beam 50 emitted from electron gun 10 is accelerated by a potential difference between cathode 11 and anode 40, and introduced into helix 20, and then travels within helix 20 while interacting with an RF signal input from one end of helix 20. Electron beam 50 which has passed through the inside of helix 20 is captured by collector 30. In this event, the RF signal is amplified by the interaction with electron beam 50, and output from the other end of helix 20.
Power supply device 60 supplies cathode 11 with a helix voltage (Ehel) which is a negative DC voltage with reference to the potential (HELIX) of helix 20. Power supply device 60 also supplies collector 30 with a collector voltage (Ecol) which is a positive DC voltage with reference to the potential (H/K) of cathode 11, and supplies heater 12 with heater voltage (Eh) which is a negative DC voltage with reference to the potential (H/K) of cathode 11. Helix 20 is generally connected to the case of traveling wave tube 1 for grounding.
Notably, while FIG. 1 shows an exemplary configuration of traveling wave tube 1 which comprises one collector 30, traveling wave tube 1 may comprise a plurality of collectors 30. Also, while FIG. 1 shows an exemplary use in which anode 40 is grounded within power supply device 60, there is also another exemplary use for traveling wave tube 1, in which anode 40 is supplied with anode voltage (Ea) which is a positive DC voltage with reference to the potential (H/K) of cathode 11.
FIGS. 2 and 3 show a detailed exemplary configuration of collector 30 shown in FIG. 1. Collectors 30 shown in FIGS. 2 and 3 are also described, for example, in Background Art of Japanese Laid-Open Patent Application No. 11-67108.
FIG. 2 is a side sectional view showing an exemplary configuration of a background art collector, and FIG. 3 is a side sectional view showing another exemplary configuration of a background art collector. FIG. 2 shows an exemplary configuration of a traveling wave tube which comprises one collector, while FIG. 3 shows an exemplary configuration of a traveling wave tube which comprises two collectors.
The traveling wave tube shown in FIG. 2 comprises closed cylindrical collector 30, where the size of collector 30 is gradually reduced in a tapering shape from the middle of the side surface toward an open end. Collector 30 is supported and fixed within an enclosure 33 of traveling wave tube 1 by insulating ceramic 32 such that the opening is oriented to electron gun 10 (see FIG. 1). Lead wire 34 is connected to the bottom of collector 30, and this lead wire 34 is drawn to the outside through collector terminal 35 disposed on enclosure 33.
On the other hand, the traveling wave tube shown in FIG. 3 comprises first cylindrical collector 301 and second closed cylindrical collector 302. The size of first collector 301 is gradually reduced in a tapering shape from the middle of the side surface toward one open end. Second collector 302 has a shape similar to that of collector 30 shown in FIG. 2.
First collector 301 and second collector 302 are supported and fixed within enclosure 33 of traveling wave tube 1 by insulating ceramic 32 such that their respective openings are oriented to electron gun 10 (see FIG. 1). First lead wire 341 is connected to first collector 301, while second lead wire 342 is connected to second collector 302.
First lead wire 341 is drawn to the outside through a gap defined in insulating ceramic 32 and first collector terminal 351 disposed on enclosure 33. Second lead wire 342 in turn is drawn to the outside through second collector terminal 352 disposed on enclosure 33.
Collector 30 shown in FIG. 2, and first collector 301 and second collector 302 shown in FIG. 3 are made of molybdenum (Mo), copper (Cu) or a composite material comprised of molybdenum and copper, and are worked into the shapes shown in FIGS. 2 and 3 by cutting plate materials or bar stocks made of these materials.
Also, collector 30 shown in FIG. 2, and first collector 301 and second collector 302 shown in FIG. 3 are formed, for example, with a copper plated layer having a secondary electron emission coefficient smaller than that of molybdenum, or a graphite layer having a secondary electron emission coefficient smaller yet than that of copper on the entire surface or part of the surface in order to restrain emission of secondary electrons due to collisions of electron beams.
Generally, it is difficult to plate copper on the surface of the collector made of molybdenum, described above, and even if the plated layer is formed, the layer has a problem in that it can be easily peeled off. This is attributable to the low bonding force of the copper plated layer with molybdenum because molybdenum does not form a stable compound with copper.
On the other hand, Graphite is a layered compound. In each layer, the carbon atoms are arranged in a hexagonal lattice. While the Carbon-Carbon bond within the plane exhibits a high bonding force due to the sp2 hybrids, planes positioned one on another exhibit a low bonding force because they are bonded with the van der Waals forces. Also, graphite includes many lattice defects in end regions, where carbon atoms are not bonded to one another, giving rise to a problem in which graphite is easily dissociated by carbon atoms in the lattice defect parts which bond with oxygen atoms, hydrogen atoms and the like. For this reason, a graphite plane might be peel off, if it is heated in a brazing operation or the like during the assembly process of a traveling wave tube. In particular, graphite is formed by dense layers, and if the base metal is copper, there is a high possibility that graphite will peel off due to the difference in the thermal expansion coefficient when it is heated.